In a current access network, there are massive network devices, such as a digital subscriber line access multiplexer (DSLAM), an optical network unit (ONU), an optical line terminal (OLT), a router, a broadband network gateway (BNG), a switch, and a broadband remote access server. When these network devices are located on a propagation path for a message, each of these network devices needs to support a function of processing an access loop identifier carried in the message. A format and contents of the access loop identifier vary slightly with each operator. Therefore, all these network devices need to be customized for different operators.